Servo system for aircraft



` June 29, 1943. A. B. HEMsrRr-:ET

I SERVO SYSTEM FOR AIRCRAFT Filed Jan. 15. 1942 z2-To Vacuum Pump T6 Vacuum Pump I INVENTOR, ALBERT B.

HEM STR EE Ti y reuma .Itas 29. 194s slsziwo sYsrEM ron AmoaAx-f'r Alben n. mmm-eet, Flushing, N. Y., mmm to Sperry Gyroscope Company. IM N. Y., a corporation of New York Brooklyn,

Applictin Jllllll'y 13, 1942, Sel'lll N0. 426,651

(Cl. 244-18) Y vertical shaft connected to the vertical ring t This invention relates to the control, through a servo system, of airplane control surfaces such as the rudder, ailerons or elevators. Such servo systems are now commonly employed in connection with automatic pilots for aircraft and are also used in large ships to assist the human pilot. A large part of the weight of such'prior systems has been in the servomotor itselfv which is usually mounted on the aircraft structure and connected to the controlling surface through suitable wires or levers. To reduce thel size, weight and expense of such servomotors, I propose to employ Flettner tabs on such surfaces so that a small, light servomotor may be employed, and to further simplify and lighten such servo system by building into the trim tab itself a pressure responsive device which moves the tab on slight diiierences in air pressure supplied within the tab from the automatic pilot or a manually operative valve on the airplane. Thus separate servomotors are virtually eliminated.v With such a device I nd it possible to operate the tab directly or indirectly from the weak pick-oil! signals received from an automatic pilot for aircraft, although I may provide air relays or boosters between the automatic pilot and the servomotor, especially where long air lines are necessary.

Referring to the drawing illustrating the preferred form of my invention.

Fig. 1 shows a diagrammatic view of the direction gyro element of an automatic pilot connected to operate the trim tab of the rudder, the former being shown in perspective view, partly in vertical section.

Fig. 2 shows a vertical section through the trim tab, showing the improved built-in servo system.

Fig. 3 is a view similar to Fig. 2, showing the resulting movement of the trim tab when superior air pressure is supplied to the upper compartment.

Fig. 4 is a front elevation of a` trim tab, the section being taken on line t-4 of Fig. 2.

Fig. 5 is a plan view, partly in section, of a modified form of the invention.

While my servo system may be operated from a manually operated controller, I have shown it operated from a standard form of automatic pilot in which the signals are in the form of diierential air pressure. Fig. 1 shows only the directional gyro element of such pilot, the directional gyro proper being shown at I, enclosed within'a casing 2 from which air is exhausted through l pipe 3 connected to a suitable vacuum pump (not shown). The differential air pressure signals are created by a cut-off disc l secured to the of the directional gyroscope. Said cut-oif'disc cooperatesA with ports 1 and 3 in a `member 3 rotatably mounted above the gyroscope on a central stem I.. The port 1 is connected throughl an annular chanel II to a pipe I2 leading toward the trim tab I3, while the port l is connected through an annular channel Il' in central stem I0 to the other pipe Il. The continuatlons I 2' and It' of said pipes are shown as made of flexible material adjacent the hinged point I5 of the main control surface I8 and also adjacent the hinged point-I1 of the trim tab I3.

It will be understood that if necessary, one or more suitable relay or booster valves, indicated diagrammatically at I9, may be employed between the gyroscope and trim-tab, especially if the pipe lines are long. to avoid too great a pressure drop in the lines. It is also'understood that I may employ, if desired, a suitable antihunt device 20 or devices as known in the prior art, such as shown in the patent to Kenyon and Zand No. 2,210,916, dated August 13, 1940, for Automatic pilots for dirigible craft. According to this system, the diaphragm or piston 2l within vthe cylinder or container 22 is connected through a piston rod 23 to rotate the pick-oil' housing 9 a slight amount in either direction, the two ends of the cylinder being connected, respectively, through restricted valves 2l, 24 to the pipes I2 and Il. The connection to the valve housing in this instance is shown in the form of a reversible Worm gear 26 Aon a stem 23 which meshes with teeth 21 on a gear secured to the valve housing 9. The course change knob is shown at 28, which has on the shaft thereof a bevel gear 29 normally out of mesh with gear 21.

As heretofore stated, I prefer to incorporate my servomotor within the trim tab I3 itself, which is pivoted to the vniairi rudder structure l@ through an anti-friction bearing 3|. As shown in Figs. 2 and 3, I secure across the middle of the interior of the trim tab a flexible diaphragm 30 and connect the extensions from pipes I2 and I4' to the interior of the tab on each side of the diaphragm, around which re-enforcing plates 34 may be placed, the plates being riveted together and hinged at one end of hinge 35 to the tab structure. A hole is cut through the tab at one side, as at 32, and there extends through this hole the bent end of a lever 38', which end is shown in the form of a bolt 33, the head of which is shown as extending through the diaphragm 3l and its re-enforcing plates 34, which separate the interior of the tab into two chambers III and I. Around the bolt I` show two sleeves 35 and 31 which clamp between them the middle portion of the fiexible sealing closure 52 around the hole. The diaphragm 30 and plates 34 are clamped between. the bolt head and lower sleeve 36. The outer end of the bolt is shown as extending through the other portion of lever 3B, the nut 39 of the bolt being clamped tightly on the same so that the lever 38, bolt and sleeves form a bellcrank structure, the outer end of which is rigidly clamped to plates 34 of the hinged stiffened dia-` that supplied by pipe I4', the trim tab will be rotated counter-clockwise, asv indicated i'n Fig. 3, because the mean effective pressure on the unlder surface of the upper wall ofthe tab exceeds that transmitted by the dividing diaphragm to the tab A however, the pressure supplied by pipe I2' exceeds due to the fact that a portion of the pressure on the latter is absorbed by the bell-crank structure. In other words, analysis will show that a portion of the downward pressure on the diaphragm is resisted by the bell-crank lever 38, this pressure being effective at hinge 40to tend to move lever 4| about its fixed axis 42. I'his results in actual movement of the tab I3 to the position in which it is shown in Fig. 3.

For similar reasons, if the superior pressure is supplied by the pipe I4', the tab will rotate clockwise. It will be obvious that the tab will move until the counter pressure of the air stream balances the unbalanced pressure within the tab, so :that movement of the tab is vobtained in proportion to the signal strength, which is in turn proportional to the deviation through a limited angle. Fig. 5 illustrates a simplified for modified form of the invention in which the :bolt structure 38A secured to the diaphragm vis .hinged to the fixed arm 45 on the structure of the main rudder through a link 46. The same action will be szecured in this case since the pressure on half ofv the trim tab will be partially borne 'by the bol-1t, so that the trim .tab will berotated 'as before.

As many changes could lbe lmadein the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not Yin a limiting sense.

Having described my invention, hat I claim and desire to secure by Letters Pa ei'rI; is: y

1. A hinged hollow control .surface for airplanes and the like, comprising a support to which said surface is hinged and having within said surface means for dividing the interior into two chambers, a linkage connected to said dividing means and exteriorly hinged to said support, and means for supplying differential air pressure within each chamber.

2. A system for controlling hinged control surfaces on large aircraft, comprising an auxiliary tab hinged to the control surface, said auxiliary tab being hollow, a diaphragm within said tab dividing it into two chambers, a link connecting said diaphragm to a point on said main control surface, and means for supplying differential air pressure within each chamber.

3. In an automatic pilot for aircraft, the combination with a position maintaining device, a differential pressure pick-off thereat giving differential pressure signals proportional to displacement, a main control surface to be controlled fromv said device, a tab hinged to said surface, a displaceable diaphragm built within said tab, means operated by displacement thereof for turning said tab, and means connecting said pick-olf and the interior of said tab for displacing said diaphragm.

L A control surface as claimed in claim 1, in which said linkage comprises a bell-crank lever connected to said dividing means at one end, and

a second lever hinged at one end to the fixed support and at its other end to said bell-crank lever.

5. In an automatic pilot for aircraft, `the combination/with a position maintaining device, a diierential pressure pick-off thereat giving primary dierential pressure signals proportional to displacement, an anti-hunt device actuated from said signals for giving a corrective displacement to said pick-off, a main control surface to be controlled from said first `mentioned device, a tab hinged Ato said surface, a displaceable diaphragm built within said tab, means operated by displacement ythereof for turning said tab, and means connecting said pick-off and the interiorof said tab for displacing said diaphragmwhereby said :tab is moved in proportion to said signals and lhuntingfis prevented.

ALBERT B. HEMS'I'REET. 

